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To improve the limited quantitative understanding of tidal hydrodynamics in Kompong Som Bay (Cambodia), we developed a three-dimensional FVCOM model for the Gulf of Thailand with local refinement in the bay and simulated April 2018–April 2019. Model performance was evaluated using a 25-hour ADCP record in the bay, supplemented by a half-month hourly tide-gauge record at Ko Lak and published K1 harmonic constants at six additional stations. The model reproduces observed tidal elevations and currents well (elevation Skill ≈ 0.99; current-speed Skill ≈ 0.80–0.95). Harmonic analysis indicates a mixed tide with strong diurnal dominance (K1/O1 > M2/S2), with semidiurnal constituents locally enhanced toward the northern inner bay. The annual-mean tidal range increases from ~0.4–0.5 m offshore to ~0.6 m in the outer bay and ~0.7 m in the northern inner bay, with maximum tidal range locally exceeding 1.2 m. Depth-averaged currents show a “strong-at-the-mouth, weak-in-the-inner-bay” structure, with peak speeds of ~0.6–0.9 m/s in bay-mouth passages and much weaker currents across the bay interior; ellipses transition from more rotary motion offshore to predominantly reversing, channel-aligned flow inside the bay. Maximum bed shear stress exceeds ~0.1 Pa mainly in inter-island passages and headlands (maximum ~0.25 Pa), whereas most of the inner bay is <0.1 Pa and nearly half is <0.05 Pa. Tide-driven residual currents inferred from harmonic decomposition are generally weak (<0.03 m/s). An auxiliary ERA5 monthly climatological wind and sea-level pressure experiment is discussed to illustrate how seasonal atmospheric forcing may modify circulation pathways. Overall, the study provides an observation-informed tidal baseline for Kompong Som Bay.